Vinyl isocyanate exists in the form of two conformers: cis and trans. The latter is lower in energy by approximately 301 cm^–1 (or 433 K). The experimental transition frequencies were summarized in
(1) K. Vávra, L. Kolesniková, A. Belloche, R. T. Garrod, J. Koucký, T. Uhlíková, K. Luková, J.-C. Guillemin, P. Kania, H. S. P. Müller, K. M. Menten, and Š. Urban, 2022, Astron. Astrophys. 666, Art. No. A50.
The analysis takes into account lower frequency data from
(2) C. Kirby and H. Kroto, 1978, J. Mol. Spectrosc. 70, 216;
and from
(3) A. Bouchy and G. Roussy, 1977, J. Mol. Spectrosc. 68, 156.
Some transition frequencies from (2) and (3) showed large residuals and were omitted from the fit in (1). The energy difference was calculated in (1).
The calculations should sufficient for all astronomical observations. Transition frequencies with calculated uncertainties exceeding 0.1 MHz should be viewed with caution.
¹⁴N hyperfine splitting may be resolvable in cold sources at low quantum numbers, but were not considered here. Thus, the partition function does not take into account the spin multiplicity of the ¹⁴N nucleus !
The partition function was calculated as a sum over the rotational levels in the ground vibrational states of both conformers assuming they are in local thermodynamical equilibrium. Individual contributions as well as vibrational correction factors for a posteriori corrections are available.
The experimental dipole moment components are from (3) and from
(4) A. Bouchy and G. Roussy, 1979, J. Mol. Spectrosc. 77, 145.